In network communications, line cards, servers, and devices therein communicate to each other across local channels in a backplane or across longer distance channels in a local area network (“LAN”) or on long haul backbone between LANs. To send data more efficiently, communication channels that link devices, and especially the long distance channels, can be designed to transmit at much higher data rates on fewer channels for a more cost-effective solution.
However, because the number of lanes changes, as does the data rate on those lanes, a gearbox chip is typically employed to interface the local channels with the long haul channels. An example would mux two local low speed lanes (“LSLs”) at a 10 gigabit per second (Gbps) rate into a single high-speed lane (“HSL”) with a 20 Gbps or higher data rate. A gearbox chip at the other end of the long haul channel, such as fiber optic trunk, will translate the data back into the LSL for local processing at its end. To do so, gearbox chips at both ends have to coordinate with each other, usually by a proprietary or industry standard protocol, to know what data belongs to which lane. In other words, data send on the first lane and the second lane on the first end should come out on the first lane and the second lane, respectively, at the other end of the long haul channel, despite their data being mixed (or muxed) together on a single channel for the long haul channel. This is called lane coherency.
One solution to maintaining lane coherency would use logic and add latency by inserting overhead data to a packet header indicating the lane to which the data belonged. Then the receiving gearbox on the other end of the long haul channel would use logic and add latency and processing ops to read the header, decide which channel the data belonged, and route it as such. Any solution to train lanes after an existing protocol is completed during initialization will add latency to the bring up. Ensuring coherency on data is critical in effective communication. Without it, data could not be transmitted reliably.